Sealing ceramic items after glaze firing

[Greg Corning]

Hello. I hope you are well.

I'm brand new at ceramics. I've made some "collars" - clay rings about eight inches in diameter and about four inches high - to put around garden plants. (This is to conserve water by keeping it right at the plants' bases.)

The bottom edge of the rings are unglazed because I learned that glazing the bottom edge would cause them to stick to the kiln shelf. I need to seal the unglazed edges so that they don't absorb water and then fracture when water freezes next winter. I don't want toxic sealants because I fear they will leach into the soil and poison the plants as well as other organisms.

Do you know of any non-toxic sealers for ceramic items?

Thank you.

[Chilly]

Hi @Greg Corningand welcome to the forum.

Depending on the clay you are using, and the temperature/time (cone) you are firing to, your clay might be vitrified, and will not need fully glazing.  Fully vitrified means minimum absorbtion.

So, every question needs another question.....

Please tell us what clay and glazes you are using, and the cone to which you are firing.

Also, my first thought was that if they collars are not vitrified, you could just bring them in for the winter - which is what I do with my mint collection that are planted in terracotta pots, so they don't freeze/fracture.  Although wouldn't have been a problem this last winter as it was so mild!

[oldlady]

might be too simple.  why not use some cement waterproofing paint on the unglazed surface and then install the collar upside down.   that way, the glaze will be at the bottom.

[Min]

I'm not getting how the design works,  I'm visualizing a clay donut/collar that is open at the top that you fill with water but if the bottom is sealed or glazed I'm not understanding how they work.

[Chilly]

9 hours ago, Min said:

I'm not getting how the design works,  I'm visualizing a clay donut/collar that is open at the top that you fill with water but if the bottom is sealed or glazed I'm not understanding how they work.

I'm visualising an open ended tube, stood on one open end.  like a mug with no bottom.  Dipped into glaze but not to the full depth.

[neilestrick]

I'm assuming these will be set into the ground at least an inch or two? I would not leave them in the ground in the winter, as the movement of the soil as it freezes may break them. Even sitting above ground I would watch out for water puddling inside them and then freezing. I'd put them in the garage or shed over winter.

[Greg Corning]

6 hours ago, Chilly said:

I'm visualising an open ended tube, stood on one open end.  like a mug with no bottom.  Dipped into glaze but not to the full depth.

Exactly. Very short open-ended cylinders, you could say. Like gigantic ceramic dog collars. (Hey maybe that would be a cute design idea.)

[Greg Corning]

16 hours ago, Min said:

I'm not getting how the design works...

Min,

They're like a dog collar sized for a jaguar's neck.

[Greg Corning]

1 hour ago, neilestrick said:

I'm assuming these will be set into the ground at least an inch or two? I would not leave them in the ground in the winter, as the movement of the soil as it freezes may break them. Even sitting above ground I would watch out for water puddling inside them and then freezing. I'd put them in the garage or shed over winter.

neilestrick,

The one prototype I've got in place seems to work fine with about 1/2 - 3/4 inch in the ground.

Hmm... Now you've got me worried about ground movement in winter. I likely won't be able to bring most of them in because I expect the plants to grow and engulf them, which means I'd have to prune so heavily to remove the collars that it might harm (some of) the plants.)

But this is worrying. The typical winter where we are (northern New Mexico, elevation about 6,000 feet [1830 meters] brings repeated cycles of freezing and thawing, as in three or five really cold days followed by many mild days with freezing nights. So yikes, these things will face many freeze-thaw cycles per winter.

[Greg Corning]

17 hours ago, oldlady said:

might be too simple.  why not use some cement waterproofing paint on the unglazed surface and then install the collar upside down.   that way, the glaze will be at the bottom.

Dear oldlady,

That sounds like a very good idea. Thank you. I'll check to see if the waterproofing paint/coat available is resistant to leaching  and, if it is, I'll try that out. Thank you.

[Greg Corning]

18 hours ago, Chilly said:

Hi @Greg Corningand welcome to the forum.

...every question needs another question.....

Please tell us what clay and glazes you are using, and the cone to which you are firing.

 

Dear Chilly,

The clay is from New Mexico Clay in Albuquerque. I am told it is a white-ish porcelaneous clay, "mid-fire". The plan was to fire it to cone 5. The glaze is just a commercial glaze - nothing at all fancy or advanced.

Thank you for asking.

[Magnolia Mud Research]

@GregCorning

sometime back I read that Val Cushing had a recipe for clay bodies that will survive freezing; it was probably in the "Cushing's Handbook".
bricks and roof tiles have survived freezing ice and melting for many years; 
none of bricks in the buildings,canals, and roads broke during the winter freezs when I lived in the Netherlands and  Germany. 
the "trick" is to have the proper porosity in the ceramics. 
glazing may not be a good idea.  

Question: how deep into the ground does the freezing penetrate?   how well does the plants cover the "dog collar".   do you cover the plants during freezing periods?   how cold is "cold"?  how dry is the soil during these cold periods. these are variables that will effect the environment and freezing/melting cycles. 

LT
 

[Greg Corning]

36 minutes ago, Magnolia Mud Research said:

@GregCorning

sometime back I read that Val Cushing had a recipe for clay bodies that will survive freezing; it was probably in the "Cushing's Handbook".
bricks and roof tiles have survived freezing ice and melting for many years; 
none of bricks in the buildings,canals, and roads broke during the winter freezs when I lived in the Netherlands and  Germany. 
the "trick" is to have the proper porosity in the ceramics. 
glazing may not be a good idea.  

Question: how deep into the ground does the freezing penetrate?   how well does the plants cover the "dog collar".   do you cover the plants during freezing periods?   how cold is "cold"?  how dry is the soil during these cold periods. these are variables that will effect the environment and freezing/melting cycles. 

LT
 

Dear LT,

Your ideas are excellent food for thought. I had not thought about various factors to consider. I'll look into the Val Cushing information. Thank you.

[Russ]

2 hours ago, Magnolia Mud Research said:

Question: how deep into the ground does the freezing penetrate?   how well does the plants cover the "dog collar".   do you cover the plants during freezing periods?   how cold is "cold"?  how dry is the soil during these cold periods. these are variables that will effect the environment and freezing/melting cycles. 

Water lines are put in at 4ft here in northern NM. Ive seen frozen ground 3ft deep. Cold? Zone 5 so it can and has got down to 20 below zero f.  Dry? Some winters we get plenty of snow others minimal.  Ive seen it snow in December,  rain in January  and back to snow in February  so we have the wackiest of weather.

So Gregg... what type of plants are you using these  collars for?

[Min]

Grinding Room Recipes from Alfred has a Cushing recipe below from page 18 of his Handbook but it's fired in reduction to cone 6. Not all the materials are available any longer.

For determining a claybodies suitability for outdoor freezing conditions you need to compare the fired clays closed (C) versus open (B) porosity.  C/B result needs to be less than 0.78 to pass CSA and ASTM ratings for outdoor use. How to do the testing in this link under "Testing a Specific Claybody". This is not the same as just measuring absorption.

[Bill Kielb]

On 6/6/2022 at 3:05 PM, Greg Corning said:

Do you know of any non-toxic sealers for ceramic items?

Epoxy would be my best guess for some longevity. Food grade epoxy if in doubt or turn them right side up, color the top as an accent and clear epoxy just the top. As far as soil pressure, no idea if it will eventually break the ring. If the soil is kept reasonably loose and aerated my total guess is they will last for quite some time and you will have to re - imbed them occasionally as the soil will push them up out of the ground over time.

[Greg Corning]

14 hours ago, Russ said:

So Greg... what type of plants are you using these  collars for?

A variety of plants... Various salvias; columbine; penstemon; lavender - ornamentals, mostly perennials.

Edited June 8, 2022 by Greg Corning
Spelling

[Greg Corning]

13 hours ago, Min said:

 

Min,

Excellent, scholarly + wise information. Thank you.

[Greg Corning]

12 hours ago, Bill Kielb said:

Epoxy would be my best guess for some longevity. Food grade epoxy ...

Learning new things! I had no idea there is something called food-grade epoxy! Thank you.

[PeterH]

Perhaps relevant:
Outdoor Weather Resistant Ceramics
https://digitalfire.com/article/outdoor+weather+resistant+ceramics
This is a common sealer available at a hardware store. I have dipped the terra cotta tile and it has dried. The surface of the dipped portion is smoother and has a slight sheen. That is the price paid for sealing the matrix against freeze-thaw spalling.

 

[Greg Corning]

On 6/8/2022 at 6:18 AM, PeterH said:

Perhaps relevant:
Outdoor Weather Resistant Ceramics
https://digitalfire.com/article/outdoor+weather+resistant+ceramics
This is a common sealer available at a hardware store...
 

 

Your article is extremely informative! Thank you.

Would the sealant leach out and contaminate the garden soil?

[neilestrick]

The other concern with leaving them on the ground is if you get a freeze-thaw cycle where the ring has a puddle in it from rain or melted snow and the re-freezes. When building outdoor ceramics you need the proper clay body, but also the proper design. Outdoor sculptures have to be designed in a way that water won't puddle into crevices where it can freeze and expand and break the piece.

[neilestrick]

On 6/7/2022 at 5:37 PM, Min said:

Grinding Room Recipes from Alfred has a Cushing recipe below from page 18 of his Handbook but it's fired in reduction to cone 6. Not all the materials are available any longer.

For determining a claybodies suitability for outdoor freezing conditions you need to compare the fired clays closed (C) versus open (B) porosity.  C/B result needs to be less than 0.78 to pass CSA and ASTM ratings for outdoor use. How to do the testing in this link under "Testing a Specific Claybody". This is not the same as just measuring absorption.

Note that this body is meant to be fired in reduction. In oxidation it's going to have different properties since the iron will behave differently.

[mr_glazy_man]

@Greg Corning I do know that some tile manufacturers will seal tiles by dipping in a silicone treatment and then left to dry.

I would reach out to the manufacturer to determine whether harmful chemicals (if there are any) from a sealing product would leach as I don’t think, without presuming, it’s within our field of expertise here.

[PeterH]

On 6/11/2022 at 4:05 PM, Greg Corning said:

Would the sealant leach out and contaminate the garden soil?

I doubt it, but am not in a position to know.

However you would only be using it to seal the unglazed edge of the collar, which would presumably not be in contact with the soil. Minimising any opportunity to leach.